Pedicle screw drivers of the relevant species substantially consist of an outer sleeve for gripping and guiding the instrument, an intermediate sleeve rotatably and movably received by the latter which is made to engage in a head of a pedicle screw as well as a multi-part shank inserted in the intermediate sleeve by which shank the pedicle screw is finally screwed together.
From the disclosure of the document US 2008/0200918 A1 a screw driver comprising an outer protective sleeve is known through the distal aperture of which an intermediate sleeve is inserted. Through a distal aperture of the intermediate sleeve in turn a shank is inserted by means of which a pedicle screw is screwed. A locking means adapted to connect the shank to the intermediate sleeve in a rotationally fixed manner so that inadvertent release of this connection is prevented after arranging the pedicle screw at the screw driver is pushed onto the shank in the axial extension of the protective sleeve at its proximal end. Accordingly, the known screw driver system is designed so that it is assembled successively from the outside to the inside by inserting each successive component to be mounted into the already mounted component through the distal aperture of the latter. As a consequence, dismounting can be carried out in the inverse order and direction only, i.e. such that the screw driver system first has to be separated from the pedicle screw so that the shank can be removed first so as to be able to subsequently dismount the locking means and finally the intermediate sleeve.
The document WO 2011/043799 describes a similar screw driver of the afore-described type for screwing pedicle screws. In this system initially an intermediate sleeve is rotatably and movably introduced into an outer sleeve via the proximal aperture thereof. A two-part initially dismounted shank is received by the intermediate sleeve. A proximal portion of the shank is introduced first via a proximal aperture of the intermediate sleeve into the same.
After that a second portion of the shank is introduced via a distal aperture of the intermediate sleeve into the same and is coupled to the first portion in a rotationally fixed manner. Only now can this system be used for arranging a pedicle screw. Then a distal thread of the intermediate sleeve is screwed to a head of a pedicle screw and the screw engaging element is clamped there between. After screwing the bone screw into the pedicle by the screw driver, the intermediate sleeve is screwed out of the head via a proximal handle and the entire screw driver can be removed while the pedicle screw remains in the body.
Usually set pedicle screws are checked by visual inspection and, respectively, radiographs and are corrected if required. Here the operating surgeon is faced with two problems. On the one hand, the view to the pedicle position is strongly restricted by the comparably bulky system comprising two sleeves each having a proximal handle as well as the shaft received therein. In addition, among various different reasons a plurality of comparatively bulky elements such as those of the screw driver are the reason for undesired artefact formations during X-raying, from which the quality of the photograph suffers and the judgment of the result is impeded. Since in the case of the known systems the screw driver can be uncoupled and removed from the body only as a whole, as a consequence the existing connection between the pedicle screw and the screw driver equally would have to be released. Consequently, for a required correction the screw driver again has to be coupled to the pedicle screw which is detrimental to the bone screw already screwed in and the connection thereof to the bone and which moreover is time-consuming.
Frequently, after screwing in a pedicle screw cement augmentation is carried out by means of cannulated screws to improve fixation thereof in the bone, especially for fixation in the osteoporotic vertebral body. In the known systems it is a drawback that the screw driver first has to be detached and a cement applicator has to be coupled to the bone screw, an injection cannula has to be fastened to the pedicle screw or another sleeve has to be inserted in the pedicle screw so that this connection withstands the pressure developed during cementing. Thus the intervention is extended in time and further cost-intensive instruments are required.
After placing two or more pedicle screws and cementing, where appropriate, it is frequently necessary to reposition the respective carriers of the pedicle screws relative to each other by distracting or compressing and to keep free an access to the operating area so that the operating surgeon is able to work largely unhindered. Points of application for carrying out manipulations are the neck of the bone screw, the outside of the body or head, the inside of the body or head or the Torx (hexagon socket) in the bone screw and, respectively, combinations thereof. Manipulations acting on the body or screw neck are not parallel. Usually parallel distraction/compression is desired, however. A parallel movement is ensured only when the bone screw is connected directly and rigidly to a parallel distractor/compressor. Several systems offer the possibility of blocking the bone screw to the body without making use of the connecting rod and the clamping screw or set screw, by pressing directly onto the insert so as then to act on the body and to be able to perform parallel distraction/compression. This course of action is by far more complicated and is not suited for rapid distraction/compression.
Moreover, in the latter system it is a drawback especially regarding smooth and precise screwing-in that no continuous shank is available. Therefore a certain degree of play always has to be accepted during screwing-in.
Since the known systems both restrict the capability of inspecting the already mounted screws and allow subsequent and usually highly necessary steps such as cement augmentation and distraction/compression by dismounting and mounting of different tools only in an intricate and time-intensive manner, there is a need for action in further developing the screw systems.